Young-Kyun Kim, Kyu-Sik Kim, Young-Beum Song, Jung Hyo Park, Kee-Ahn Lee.Ģ.47 GPa grade ultra-strong 15Co-12Ni secondary hardening steel with superior ductility and fracture toughness Xiaopei Wang, Yoshiaki Morisada, Hidetoshi Fujii.įlat friction stir spot welding of low carbon steel by double side adjustable tools Liu, Fundamentals of Materials Science, Northwestern PolytechnicalUniversity Press, Xi’an, 2011, pp. Moreover, the microhardness of the three solidified alloys reaches the maximum when the undercoolings are 185 K, 270 K and 316 K, respectively. Meanwhile, for the Ti-(47, 50) at.% Al, the transformation temperature of metastable intermediate α phase decreases with the increase of undercooling. In the process from low undercooling to high undercooling, the primary phase of undercooled Ti-54 at.% Al alloys changes from α-Ti (α) to γ-TiAl (γ) and the microstructures of solidified alloys evolve from spherical primary dendrites and matrix phases to cellular dendrite phases. When Δ T rises, the microstructures of solidified Ti-50 at.% Al alloys appear from coarse primary dendrites and interdendritic dendrites to refined lamellar dendrites. The microstructures of solidified Ti-47 at.% Al alloys successively appear as coarse lamellar dendrites and finally evolve to refined parallel lamellar dendrites with the increasing undercooling. Three recalescences are found at all undercoolings for Ti-47 at.% Al alloy and at high undercoolings for Ti-50 at.% Al alloy. Besides, a novel formula with physical meaning is proposed to explain that the more ordered liquid metal atoms accelerate the primary dendrite growth. The primary dendrite growth velocity V meets a double exponential relationship with the undercooling Δ T. Recalescence processes corresponding to the primary dendrite growth and subsequent phase transition were recorded at various undercoolings. The maximum undercoolings of the three liquid alloys were 376 K, 352 K and 316 K, respectively. The rapid solidification processes of undercooled Ti-(47, 50, 54) at.% Al alloys were investigated by electromagnetic levitation (EML) method combined with a high-speed photoelectric detector.
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